Hot gas defrost refrigeration system

ABSTRACT

A control system for controlling the individual defrosting of a plurality of evaporators connected to a common refrigeration system wherein the defrosting is accomplished by the use of hot gas from the refrigeration system. The need for defrosting of a particular evaporator is called for either on demand by a frost sensor associated with the evaporator or by time by a time control. A sequential control apparatus is used to schedule the defrosting operation of the evaporators when they are defrosted on demand to limit the number of evaporators that are being defrosted at any particular moment as a limited amount of hot gas is available from the refrigeration system.

United States Patent Stanton July 15, 1975 HOT GAS DEFROST REFRIGERATION SYSTEM Primary Examiner-Meyer Perlin [75] Inventor: David .I. Stanton, New Brighton, f Agent or firm-Henry Hanson; Clyde Blmn Minn.

[73] Assignee: Honeywell lnc., Minneapolis, Minn. {57] ABSTRACT [22] FiI d; J 29, 1974 A control system for controlling the individual defrost- 2 l] Appl. No.: 492,382

[52] US. Cl. 62/155; 62/157; 62/l96; 62/278 [51] Int. Cl. F25b 47/00 [58] Field of Search 62/l40, 157, 158, l96, 62/278, l55

[56] References Cited UNITED STATES PATENTS 3.316.731 5/1967 Quick 62/278 3,638,444 2/l972 Licdahl 62/278 FlRST SET OF EVAPORATORS ing of a plurality of evaporators connected to a common refrigeration system wherein the defrosting is accomplished by the use of hot gas from the refrigeration system. The need for defrosting of a particular evaporator is called for either on demand by a frost sensor associated with the evaporator or by time by a time control. A sequential control apparatus is used to schedule the defrosting operation of the evaporators when they are defrosted on demand to limit the number of evaporators that are being defrosted at any particular moment as a limited amount of hot gas is available from the refrigeration system.

8 Claims, 2 Drawing Figures moron compnzssoa AND TO omen ewwoaxroas m ssr conoeusaa TO sscouo ser or i) 40' EVAPORATORS oil! I APonA'rons 33 .1 l zir 46 i l l 3cm x o o 6 e (j I 47 a l7 9 Q 9 l l l l I I b A l 5 TIMER CONTROL 49 SHEET 1 FIRST SET OF EVAPORATORS 2 III MOTQR CQMPRESSOR AND CONDENSER TO OTHER EVAPORATORS IN SET TO SECOND SET OF EVAPORATORS APORATORS O A THIRD SET TlMER CONTROL 49 FlG.l

1 HOT GAS DEFROST REFRIGERATION SYSTEM BACKGROUND AND SUMMARY OF THE INVENTION In refrigeration systems having a plurality of evaporators connected to a compressor system, a defrosting operation making use of hot gas from the compressor system is commonly done by the use of valves to reverse the refrigeration flow so that hot gas normally passing to the condenser flows through the evaporator to heat the evaporator and remove any frost. To accomplish such in one prior art system which has a number of evaporators having frost sensors to provide an output should an evaporator or set of evaporators need defrosting, an interlocking relay circuit is used. When one frost sensor for a particular set of evaporators initiates a defrosting operation to deliver hot gas to that set of evaporators, the circuit is modified to prevent any other frost sensor for other sets of evaporators from being capable of initiating a defrost cycle. The interlocking relay circuit limits the amount of hot gas which is drawn from the compressor system for defrosting to only one set of evaporators at a time; however, such an interlocking relay circuit is complex and expensive.

The present invention is concerned with an improved control system for controlling the individual defrosting operation of each of a plurality of evaporators or sets of evaporators connected to a common compressor system. The evaporators are defrosted either in accordance with a time schedule by a time control or upon demand by a frost sensor responsive to the frost on the evaporator. To provide for only one defrosting operation to take place at a time, a sequential control apparatus has a plurality of output circuits for scanning and individually initiating the defrost cycle of any one of the sets of evaporators which needs defrosting from a frost sensor. The sequential control apparatus upon initiating the defrosting operation of one set of evaporators is then stopped until that particular set of evaporators is defrosted, at which time, the sequential control apparatus steps to the next evaporator for its defrost operation. If a defrost operation is initiated by the time control, the sequential control apparatus is inhibited to prevent further demand defrost operations while the time controlled defrost operation takes place.

FIG. I is a schematic showing of the refrigerstion system with controls for hot gas defrosting.

FIG. 2 is a wiring diagram of the sequential control apparatus.

DESCRIPTION OF THE INVENTION Referring to FIG. I, a refrigeration system of a conventional type which has a plurality of evaporators 11 and 12 and a motor compressor and a condenser or compressor system 13 provides cooling to a number of cold storage boxes or spaces each of which having evaporators through which air is blown by an associated fan. Evaporator 11 is associated with a first set of evaporators. Evaporator 12 is associated with a third set of evaporators. From time to time as frost builds up on the evaporators, a defrosting operation must be initiated. In this particular system which has a large number of evaporators, the defrosting of an evaporator or set of evaporators is accomplished in a conventional manner by energizing solenoid valves to reverse the refrigeration flow to deliver hot gas to the evaporator for raising its temperature and thus melting off the frost.

Evaporator 11 may have other evaporators connected in parallel with/or without frost sensors as only one evaporator in a set need have a sensor, the others being slave units. Similarly, evaporator 12 may be a single evaporator or connected in a third set. The number of evaporators and/or sets of evaporators connected in the compressor system 10 can vary for every installation. Since a plurality of evaporators are connected in the system, the number to be defrosted by hot gas is limited to the amount of hot gas available. Thus only a selected number of evaporators can be defrosted at one time. Whether a defrosting operation need be initiated for a particular evaporator is determined by either the use of a frost sensor or by time selection using a timer.

Evaporator 11, as well as others in the first set, has a frost responsive or sensor apparatus 14 of the type shown in the Clifford L. Sandstrom et al. US. Pat. No. 3,453,837 issued July 8, I969 having a pair of air temperature sensors 15 and 16 responding to air temperature difference between the upsteam and the downstream air through the evaporator ll. A demand defrost operation output signal is provided on conductor 17 to the input of a conventional relay 20 through a diode 21. By means of diode 21 and several other diodes 21, 21" and 21', a plurality of temperature sensors (not shown) for other evaporators of the first set, can be connected to the input of relay 20 and only one sensor controls the relay as the other diodes are back biased. Upon the presence of an input signal to relay 20, relay contact 22 is closed to provide an input on a circuit 23.

A sequential control apparatus 30 contains a stepping switching device or sequencer 3! which is schematically shown to have a member move along a plurality of output circuits or contacts 32, 33, 34, etc. to provide output signals in a sequential manner. Output circuit 32 is connected to a second input 35 of a NAND gate 36 of a relay or switching device 40. A second input of gate 36 is connected to circuit 23. Upon gate 36 receiving inputs over both circuits 23 and 35, relay 40 is energized and switching circuits 4] and 42 are adapted to control valves 43 and 44 respectively. Upon the operation of relay 40, valves 43 and 44 provide for the termination of refrigerant flow to evaporator I] as well as others in the first set and for the flow of hot gas for the defrost cycle.

While only one such set of valves 43 and 44 are shown, relays 40, 40" and 40' are similarly connected to receive inputs from both frost sensor and control 30 to terminate the flow of refrigeration and initiate the flow of hot gas to other sets of evaporators. For explanation purposes, the operation of the sequential control apparatus 30 with one particular relay 40 is shown.

Relay 40 has a feedback circuit 47 connected to input 48 of sequential control apparatus 30; so that, when relay 40 is energized to provide for the defrosting operation, the feedback circuit stops the operation of apparatus 30. Sequencer 31 then maintains an output on circuit 32 until the defrost operation associated with the evaporator of relay 40 is terminated. Upon the termination of the defrost cycle to de-energize relay 40, the feedback signal on circuit 47 is removed and sequential control 30 steps to the next circuit 33 for relay 40' and another set of evaporators. NAND gate 36 has a feedback circuit 46 connected to sequential control 30 for maintaining a defrost cycle in progress.

Evaporator 12 while connected to the same compressor system has its defrost operation controlled by a conventional time control or timer 49 having as a part a switching device or relay 50 which upon being energized controls the operation of valves 51 and 52 to terminate refrigerant flow and to provide for the flow of hot gas to evaporator 12 for a predetermined period of time to defrost the evaporator. Timer 49 has a plurality of switches which operate in accordance with some preset time setting to operate a series of relays similar to relay 50 for controlling valves of other evaporators. If a time controlled defrosting operation of some evaporators is provided which may not always be the case, relay 50 has a circuit 53 connected to the input of sequential control to provide for inhibiting the operation of sequencer 31 as long as the defrost operation of a evaporator such as 12 by timer 50 is in operation. Such a connection 53 between relay 50 and sequential control 30 provides for no demand defrost operation, such as by relay 40, in the system while a time defrost operation is being accomplished by timer 50. Circuits 32, 33 etc. of the sequential control 30 are inhibited to prevent a defrost operation on demand by a sensor if timer 49 has provided for the defrost operation of a set of evaporators through relay 50.

Referring to FIG. 2, the sequential control apparatus 30 and relay 40 are shown in more detail. Relay 40 has NAND gate 36 to which input circuit 23 and are connected, both of which must be energized in order to energize relay 40. Relay 40 has a pair of switching circuits or relays 41 and 42 to control valves 43 and 44. Connected intermediate NAND gate 36 and relay 41 is a conventional timing circuit 52 to provide a time delay in the de-energization of relay 41 once the input signal is removed from the NAND gate 36. Timing circuit 52 is adjustable by various values of resistor 56 to provide for selected time delay periods. The time delay provides for a delay in the operation of refrigeration valve 43 until the evaporator coil has had sufficient time to drip dry of the moisture after the defrosting operation.

Sequential control apparatus 30 comprises a conventional binary counter 54 such as 'I'I'L Logic 7493 connected to a conventional ECU to decimal converter 55 such as TTL Logic 74154 for providing for the energization of the output circuits 32, 33, 34, etc. in a sequential manner. Input circuit 47 provides for the deenergization of counter 54 when relay 40 is energized. While only one relay is shown in FIG. 2, inputs from the other relays 40', 40", 40", are obtained over circuit 62.

Relay 50 which is operated by timer 49 to control a time controlled defrost operation of certain evaporators, has an input 53 to sequential control 30 for terminating the operation of control 30 whenever a time defrost operation is taking place. Specifically feedback circuit 46 and circuit 53 are connected to the strobe control circuit 60 of converter 55. If a demand defrost operation is taking place as evidenced by a feedback on circuit 46, the output on 46 overrides the effect of the timer output on 53. The time defrost can not terminate the present output of converter 55 to circuit 32 until the demand defrost operation is completed. If the system has no time controlled defrost control of evaporators, input 53 is not used.

OPERATION OF THE INVENTION As previously mentioned, the sequential control apparatus 30 provides for the energization of only one defrosting operation at a time when the particular evaporator connected to a refrigeration system calls for demand defrost as determined by a frost sensor.

As the sequential control apparatus scans the various relays 40, 40', etc., any one of the relays which has an input signal from at least one frost sensor is energized to bring about a defrosting operation. To prevent a drain on the compressor system by having more than a limited number of evaporators in a defrosting operation at one time, as only a limited amount of hot gas is available, only one set of evaporators is defrosted depending on which output circuit of control 30 has an output.

For the call for defrosting operation of evaporator 11, sensor 14 has an output on circuit 17 to provide for the energization of relay 20 to place a signal on circuit 23 to the input of NAND gate 36; however, even though the frost sensor 14 calls for a defrosting of evaporator ll, nothing will take place in the refrigeration system until the sequential control 30 selects that particular relay 40 by the energization of circuit 35. At that time, sequential control 30 is stopped by the signal over circuit 47 and the defrosting of evaporator 11 is accomplished by the hot gas delivered through valve 44. Upon the termination of the defrost cycle as determined by the sensor 14, relay 40 is de-energized to terminate the flow of hot gas to the evaporator and after a selectable predetermined time delay determined by circuit 52, refrigeration valve 43 opens to restore normal refrigeration operation. Circuit 47 is then deenergized and sequential control 30 advances to the next relay which is shown as 40' in FIG. 1.

At anytime there is a time controlled defrost of the evaporators of the third set such as evaporator 12, timer relay 50 provides a signal over circuit 53 which may be connected to inhibit the output of sequencer 30 and prevent a start of a demand defrosting operation. Any demand defrost operation in progress will continue as a result of the signal on circuit 46 which overrides the effect of the signal on circuit 53.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. In a control system for controlling the individual defrosting of at least one of a plurality of evaporators connected to a compressor system wherein the defrosting is accomplished by the use of hot gas from the compressor system,

frost sensor means adapted to be connected to each of at least two of a plurality of evaporators of the refrigeration system for providing an output signal upon the need of defrosting of one of the evaporators,

sequential control means having a plurality of output circuits for scanning and for individually initiating a defrost cycle of any one of the two evaporators which needs defrosting,

a plurality of relay means each having two input circuits and an output circuit, said relay means is energized when each of said input circuits receive input signals, and

circuit means connecting said output signal of each of said frost sensor means to one input of a respective relay means and one of said output circuits of said sequential control means to a second input of said relay means whereby upon a frost sensor means of one evaporator having an output to demand defrost, said relay means is energized when said sequential control means provides a signal to said relay means,

said output of each of said relay means being adapted to control valve means in the compressor system to means has an input from the timer means. 7. In a control system for controlling a selective demand defrost operation of individual sets of evaporators connected to a refrigeration system by furnishing provide a hot gas defrosting operation for one of 5 hot gas to a particular set of evaporators the evaporators at a time depending upon a demand for defrosting operation by said frost sensor means and said signal of said sequential control means while normal operation of the other evaporator is maintained. 2. The invention of claim 1 wherein each of said relay means has a second output circuit connected to said sequential control means to inhibit other outputs on said output circuits of said sequential control means until a defrosting operation for the one evaporator is completed. 3. The invention of claim 1 comprising input circuit means connected to said sequential control means adapted to receive an input from a timer means controlling the defrosting operation of other evaporators to inhibit said sequential control means when a time defrost operation is initiated. 4. The invention of claim 1 wherein said output circuit of said relay means is adapted to close a refrigeration solenoid valve and open a hot gas solenoid valve when a defrosting operation is needed and comprising time delay means connected in said output circuit so that upon a termination of the defrosting operation said relay means is adapted to close the hot gas solenoid, and after a predetermined time to allow for the evaporator to drip free of water, said relay means is adapted to open the refrigeration solenoid valve. 5. The invention of claim 1 wherein said sequential control means is a BCD to decimal converter circuit for sequentially providing outputs on said output circuits. 6. The invention of claim 3 wherein each of said relay means has a second output connected to said sequential control means to maintain a demand defrost operation already initiated even though said input circuit of said sequential control a plurality of frost responsive means adapted to be connected to respond to the need of a defrosting operation of individual sets of evaporators,

sequential control means having a plurality of output circuits upon which an individual output is provided in a sequential operation manner,

a plurality of relay means each of which is adapted to control the delivery of hot gas to one set of evaporators,

circuit means connecting each of frost responsive means for one set of evaporators to one of said relay means and one of said output circuits of said sequential control means to said one relay means, whereby upon said first responsive means of a set of evaporators providing an output said relay means is energized when said sequential control means output is available, and

circuit means connected between each of said relay means and said sequential control means to inhibit said sequential operation once a defrosting operation of a particular set of evaporators is started until said relay means is de-energized at which time said sequential control operates in a sequential manner to the next relay means.

8. The invention of claim 7 wherein said sequential control means has an input circuit adapted to be connected to a timer control for controlling the time controlled defrosting operation of other evaporators connected to the compressor system,

said input circuit upon receiving an input signal, indicative of a time controlled defrost operation taking place, inhibits the sequential operation of said sequential control means to stop any further demand defrost operation of other sets of evaporators. 

1. In a control system for controlling the individual defrosting of at least one of a plurality of evaporators connected to a compressor system wherein the defrosting is accomplished by the use of hot gas from the compressor system, frost sensor means adapted to be connected to each of at least two of a plurality of evaporators of the refrigeration system for providing an output signal upon the need of defrosting of one of the evaporators, sequential control means having a plurality of output circuits for scanning and for individually initiating a defrost cycle of any one of the two evaporators which needs defrosting, a plurality of relay means each having two input circuits and an output circuit, said relay means is energized when each of said input circuits receive input signals, and circuit means connecting said output signal of each of said frost sensor means to one input of a respective relay means and one of said output circuits of said sequential control means to a second input of said relay means whereby upon a frost sensor means of one evaporator having an output to demand defrost, said relay means is energized when said sequential control means provides a signal to said relay means, said output of each of said relay means being adapted to control valve means in the compressor system to provide a hot gas defrosting operation for one of the evaporators at a time depending upon a demand for defrosting operation by said frost sensor means and said signal of said sequential control means while normal operation of the other evaporator is maintained.
 2. The invention of claim 1 wherein each of said relay means has a second output circuit connected to said sequential control means to inhibit other outputs on said output circuits of said sequential control means until a defrosting operation for the one evaporator is completed.
 3. The invention of claim 1 comprising input circuit means connected to said sequential control means adapted to receive an input from a timer means controlling the defrosting operation of other evaporators to inhibit said sequential control means when a time defrost operation is initiated.
 4. The invention of claim 1 wheRein said output circuit of said relay means is adapted to close a refrigeration solenoid valve and open a hot gas solenoid valve when a defrosting operation is needed and comprising time delay means connected in said output circuit so that upon a termination of the defrosting operation said relay means is adapted to close the hot gas solenoid, and after a predetermined time to allow for the evaporator to drip free of water, said relay means is adapted to open the refrigeration solenoid valve.
 5. The invention of claim 1 wherein said sequential control means is a BCD to decimal converter circuit for sequentially providing outputs on said output circuits.
 6. The invention of claim 3 wherein each of said relay means has a second output connected to said sequential control means to maintain a demand defrost operation already initiated even though said input circuit of said sequential control means has an input from the timer means.
 7. In a control system for controlling a selective demand defrost operation of individual sets of evaporators connected to a refrigeration system by furnishing hot gas to a particular set of evaporators a plurality of frost responsive means adapted to be connected to respond to the need of a defrosting operation of individual sets of evaporators, sequential control means having a plurality of output circuits upon which an individual output is provided in a sequential operation manner, a plurality of relay means each of which is adapted to control the delivery of hot gas to one set of evaporators, circuit means connecting each of frost responsive means for one set of evaporators to one of said relay means and one of said output circuits of said sequential control means to said one relay means, whereby upon said first responsive means of a set of evaporators providing an output said relay means is energized when said sequential control means output is available, and circuit means connected between each of said relay means and said sequential control means to inhibit said sequential operation once a defrosting operation of a particular set of evaporators is started until said relay means is de-energized at which time said sequential control operates in a sequential manner to the next relay means.
 8. The invention of claim 7 wherein said sequential control means has an input circuit adapted to be connected to a timer control for controlling the time controlled defrosting operation of other evaporators connected to the compressor system, said input circuit upon receiving an input signal, indicative of a time controlled defrost operation taking place, inhibits the sequential operation of said sequential control means to stop any further demand defrost operation of other sets of evaporators. 